The present invention relates to a device to evaporate volatile substances, in particular insecticides and/or aromatics according to the introductory clause of claim 1. Devices for evaporation are generally known. For example, evaporation devices are known where a small plate is introduced into an evaporation device which is impregnated with an active ingredient and heated in order to evaporate the active ingredient. Furthermore a method is also known by which a container containing a volatile substance is introduced into a housing of an evaporation device. This container comprises a wick that conveys the substance to be evaporated by means of capillary action out of the container. Whereby the wick end protruding from the container is located next to a heating element such as e.g., a ceramic block, so that the substance is evaporated through the heat radiated by the ceramic block. The evaporated substance can escape from the housing into the environment through aeration slits in the housing.
Another example, an evaporation device for volatile substances, in particular insecticides and/or aromatics, is known from EP 0 943 344 A1 that includes a housing with a heating unit installed therein. The heating unit comprises a heating block made of a ceramic material connected via electric lines to a connection plug located on the housing. An electrical resistance element is contained in the housing to heat the heating block. A container connected to the housing, for a substance to be evaporated, whereby a wick can be inserted into the container; with the container being connected to the housing. The wick is associated with the heating unit for the evaporation of the substance in the container by a wick end protruding from the container into the heating element. The evaporation device includes a plug-in part with a connection plug. The plug-in part is provided with threads and is inserted into the housing in which the container is disposed. Pin openings are provided on the housing into which snap-in pins are inserted in such manner that they engage the threads of the plug-in part. The distance between the heating unit carried by the plug-in part and a wick end protruding from the container can be changed by turning the plug-in part. In an embodiment of this system the plug-in part can furthermore be mounted in an eccentric manner in the housing, so the relative distance between the wick end and the heating unit can be changed in function of the desired degree of evaporation. The heating unit includes a ceramic block with an electric resistance element. Commercially available, relatively large as resistance elements are used. This leads to a relatively large heating unit and thereby also a great space requirement of the housing surrounding the heating unit and of the overall evaporation device. Such space-consuming evaporation devices are less attractive visually and can disturb the general visual effect, e.g. in a living room. In addition the design employs a great number of components which leads to large which is also relatively expensive and complicated to manufacture.
Furthermore the evaporation temperature cannot be sufficiently regulated because of the utilization of commercial resistance elements and this may have a negative effect on the flammability of certain parts or of the entire evaporation device, and possibly also on the degree of evaporation. A similar design with the above-mentioned disadvantages is also known from WO 98/58692 and EP 0 962 132 A1.
Accordingly, an object of the present invention is to create an inexpensive evaporation device for the evaporating of volatile substances, such as insecticides and/or aromatics, or relatively small dimensions in which the evaporation temperature can be accurately regulated according to the substance to be evaporated.
The above objectives are accomplished according to the present invention by utilizing the electric resistance element to constitute a heating unit of small size and thereby to provide an overall miniaturized of the evaporation device, preferably, the heating element includes a rod-shaped resistance body coated at least in some areas with a resistance layer that is cut and/or ground into certain areas for the selection of a given resistance value corresponding to the composition of the substance to be evaporated.
A resistance element of this type for heating units can advantageously be of relatively small size so that the heating block, the heating unit, and the entire housing containing the heating unit may have a relatively small size. In this manner, miniaturized evaporation devices can be had with which one or two or more suitably adapted low-volume containers may be accommodated in the housing. Due to the reduced expenditure for material and components, the miniaturized evaporation device can be produced relatively simply and inexpensively as a disposable item.
Another important advantage of an evaporation device according to the invention is that the evaporation temperature can be adjusted optimally according to the composition of the substance to be evaporated. Advantageously, the resistance layer for a given resistance value may be cut or ground in the element at different locations. The danger of flammability of the device is thus reduced and the possible negative effect on the degree of evaporation can be avoided.
There are, in principle, different ways for notching or grinding the resistance layer in order to provided a desired resistance value. In a preferred embodiment, the resistance layer is cut into and around the rod-shaped, preferably cylindrical, resistance body in a helicoidal form, such as by helicoidal laser cutting. With such a helicoidal cut the resistance value can be adjusted very precisely and easily for optimal evaporation performance.
The resistance layer can, in principle also be made of different materials, e.g. in form of a special metal layer. In an especially preferred embodiment, the resistance layer is however made in form of a metal oxide layer, preferably a nickel-chrome alloy layer. Such a metal oxide layer may be advantageously burned on thermo-chemically, e.g. by vacuum metallizing or cathodic sputtering in form of a thin layer. When the resistance layer has been applied, it is preferably subjected to a thermal process in order to stabilize the resistance layer. In addition, or alternately, the resistance body can be made of ceramic, preferably with a high content in AL2O3 (aluminum oxide), so that an especially good heat conductivity of the resistance body and thereby of the resistance element overall is achieved. The content in AL2O3 depends on the actual installation conditions e.g. the housing material, the wick material, etc. being used.
Advantageously, metal caps may be placed on the ends of the coated, rod-shaped resistance body, which are preferably pressed on. An electrical line is preferably welded to each of these caps and is in turn connected to the connection plug. Copper wire with good electrical conductivity is preferably used for the electric lines. A good electrical contact with the resistance layer is furthermore easily and reliably achieved with the metal caps. In principle several ways exist for the installation of the rod-shaped resistance element on the heating block. In an advantageous embodiment, the rod-shaped resistance element can be inserted into a recess in the heating block. The resistance element is encapsulated in the recess using there in a highly heat-conductive material in order to fix the resistance element securely in the heating block. The encapsulating material may have a great heat conductivity may be a flame-resistant insulation cement. Furthermore a slit is preferably formed on either side of the resistance element, at the opposite ends of the recess, whereby the electrical lines can be routed out of the heating block to the connection plug. With a design of this type the resistance element can easily be inserted into the recess during assembly, e.g. also using a clamping lock, so that the resistance element cannot slip during the encapsulating process. In addition, electric lines can easily be curved in the direction of the connection plug. The electric lines can be insulated in a conventional manner.
An advantageous, compact design can be provided by making the length of the resistance element, as seen in the longitudinal direction of the recess approximately equal to the width of the heating block. In this case, the electric lines may be bent at the caps approximately at right angles to the resistance element. The lines may then extend approximately parallel to each other and approximately in line with the two plug-in connections of the connection plug. Such an alignment of the electrical lines achieves an especially compact design of the heating unit, and this contributes in minimizing the size of the housing and the entire evaporation device.
In yet another aspect of the invention, a wick opening, preferably a passage hole or a traversing indentation on the edge of the heating block is formed into which the wick end extends is formed in the heating block next to the electrical resistance element. By means of such a wick opening a simple and reliable attribution of the wick end to the heating block and thereby to the heating unit is possible, and this contributes in ensuring effective evaporation.
An especially easy and rapid assembly of the heating unit in the housing is possible by providing the housing in at least two parts, an upper shell and a lower shell. The upper and lower shells can be connected to each other by means of a snap-in and/or clipping elements. Preferably, the connection means, e.g. snap-in elements, to are formed in the lower shell. At least one of the two shells is provided with aeration slits to let the evaporated substance escape into the environment. The aeration slits may be located above the wick end in the upper shell. Such a two-part housing can be produced very simply and inexpensively.
The connection plug preferably includes a base plate from which the plug pins extend to which the electric lines are connected. The base plate together with other components may be located in the housing and clamped between the upper shell and the lower shell for a strong, and thus chatter-free fixed positioning. This makes a design of great value which is overall very stable, as well as secure in fixing the components in predetermined positions.
In order to give the evaporation device a visually more esthetic aspect, a decorative element can be attached to the upper shell. A surrounding edge border is preferably formed on the upper shell, to which such a decorative element can be snapped or clipped on. Such a decorative element could for example be in form of a flowering blossom.